1. Field of the Invention
The present invention relates to a processing-free type lithographic printing plate material and, more particularly, to a processing-free type lithographic printing plate material which can be mounted, after exposure, on a printing press without any processing to conduct printing. In this specification, both the material for preparing a lithographic printing plate and the lithographic printing press plate prepared from the material are called "lithographic printing plate," for simplicity and as is common in the art.
2. Description of the Prior Art
Heretofore, as lithographic printing plates, those which are called deep-etch plates and PS (presensitized) plates have enjoyed the most popularlity. Deep-etch plates are obtained by coating a negative type light-sensitive resin on a grained Al or Zn plate and printing thereon a positive original. After development-processing, the plate is etched or a tincture applied thereto without etching, and then, after applying thereto a lacquer, removing the light-sensitive resin layer hardened by exposure. On the other hand, PS plates have a constitution in which a light-sensitive resin is coated mainly on an aluminum plate. Press plates can be prepared therefrom by printing thereon a positive or negative original and, after development processing, applying a developing ink or a protective lacquer to the hardened light-sensitive resin layer constituting image areas. As is described above, PS plates have the advantage in that several processing steps can be omitted in obtaining press plates as compared with deep-etch plates. However, a developing step and the like are still required.
Processing-free type lithographic printing plates have been suggested which enable the processing steps of lithographic printing plates after exposure to be omitted and printing to be conducted by directly mounting the exposed plates on a printing press without any chemical processings. In this specification, the term "processing-free" is used in the above-described sense. U.S. Pat. No. 3,650,743 describes this type of lithographic plates in detail. According to the disclosure, the process for preparing a lithographic printing plate involves using an electromagnetic radiation-respondent member having a three-layered structure (each layer being intimately adhered to each other) comprising a metallic first layer, a second layer of a material capable of reacting, upon being exposed, with the first layer to form a mutual reaction product, and a third layer of a material which does not react with the second layer. The process comprises exposing the second layer to an image using electromagnetic radiation through the first or third layer to thereby selectively form the mutual reaction product, thus imparting to the areas where the reaction product is formed a hydrophilicity-to-oleophilicity relationship different from that at the remaining unreacted areas.
In this process, the light-sensitive layer of the light-sensitive material to be used has a two-layered structure comprising a first layer and a second layer, as disclosed above, and extremely toxic materials such as arsenic trisulfide, arsenic pentasulfide, etc., are used as a light-sensitive element. Therefore, this lithographic printing plate can not be said to be desirable due to the toxicity of the materials used and the multi-layered structure.